The invention concerns a burner for a rotary tubular kiln with an annular channel arranged within the burner housing pipe for the pneumatic transport and blowing out of fine-grained solid fuel through an annular gap nozzle, and with a number of jet air nozzles arranged concentrically around the circumference of the annular gap nozzle with nozzle openings divergent to the burner axis, through which combustion air is emitted, divided into a large number of separate, individual high-speed primary air jets.
Common rotary kiln burners are mostly designed as so-called three-channel burners (e.g. DE 43 19 363 A1), in which a pneumatically transportable solid fuel such as coal dust flows through the central burner channel, is emitted through an annular gap nozzle, and in which the coal dust emitted at a divergent angle in the form of a cone jacket is surrounded radially on both the inside and outside with primary air as the combustion air. The primary air channel located radially within the coal dust channel has at its mouth a spin-generator, so that the primary air emitted is given a rotation component, and is also referred to as twist, swirl or radial air. Common spin-generators are generally not adjustable, at least not when the rotary tubular kiln is in operation.
The combustion air of the rotary kiln burner radially outside the coal dust, also referred to as jet air, is divided by means of a number of individual nozzles arranged in the annular jet air channel into a number of individual high-speed primary air jets, which produce a low-pressure region in their vicinity, i.e., the many high-speed primary air jets act as driving jets in accordance with the injector principle, by means of which the large mass of practically stationary secondary air surrounding the rotary kiln burner, at a temperature of around 1,000° C., is drawn in in the direction of the core of the burner flame, where intensive mixing of the hot secondary air with the coal dust emerging from the annular gap nozzle takes place, which should be burnt quickly and completely by forming an assisted, short hot flame. For the purposes of adjustment of the divergence angle of the jet air streams, the cylindrical nozzle bodies with the nozzle holes set at an angle to the nozzle axis, can be individually turned, although not when the rotary kiln is in operation, so that the optimum coal dust-jet air mixture or flame shape cannot be adjusted when the kiln is in operation by adjusting the divergence angle of the jet air streams.
EP 0 642 645 B1 describes a rotary kiln burner in whose primary air channel flexible metallic air hoses with their nozzles are arranged around the circumference, and whose air flow direction can be set from axial to radial by means of turning the complete air hose assembly consisting of the flexible air hoses with their air outlet nozzles at an angle to the burner axis in order to increase the spring component of the radial air. Apart from the fact that this known spin-imparting device for a rotary kiln burner is comparatively complicated, this known design enables only the parallel outflow of fuel and primary air, even if the primary air is given a spin component. With this known air hose system, it is not possible to set or adjust a cone-shaped divergence angle of the primary air, i.e., to make the primary air emerge as a conical envelope with such a divergence angle as to ensure the optimum mixing of the fuel cone with the primary air cone with the greatest possible flame turbulence.